The White Dwarf Evolution Code Revamped Agnès Bischoff-Kim

Penn State Worthington Scranton, Dunmore, PA 18512, USA • Static models of White Dwarfs • Not a stellar evolution code • But fast (under 15s/model) • Chemical profiles are input • Used for asteroseismology • Original code from 1970’s *1+ • Fortran code

Quick facts

What’s New

• New EOS and opacities, from MESA [4] (version 8118) • More freedom in setting the chemical profiles (Helium is

allowed in the core, Oxygen in the envelope)

Figure 2 Chemical profiles used in the comparison test (dashed – LPCODE, solid – WDEC). This is as close as we can make them. WDEC only includes 4 elements, while the LPCODE also includes trace elements.

Comparison with LPCODE

We used models posted online [5] to run a comparison test. We used the 0.593 MSun, 11288.348 K, logMH = -4.285 model and reproduced it best we could with WDEC (Figure 1). That included calibrating convection to reproduce the depth of their convection zone. (α = 1.3 was used). We calculated periods for this model and compared them to LPCODE’s.

Periods across the board (l=1, l=2, low k to high k) differ by 2.3 ± 1.4 %.

Figure 3 Brunt-Väisälä frequency profiles (dashed – LPCODE, solid – WDEC). The core bumps, corresponding to the oxygen abundance profile, are right on top of one another, consistent with the fact that the oxygen profiles are identical.

Getting a copy of the new WDEC In the future, the code and documentation will be licensed and placed on Github. Until then, email axk55@psu.edu for a copy and preliminary documentation.

Background

Originally, WDEC referred solely to a white dwarf structure and evolution code. Output from WDEC was used as input into a stellar pulsation code to obtain non-radial g-mode oscillation periods for the models [2]. In the 1990’s, the two (technically three) codes were combined into a single Fortran function for use in asteroseismic fitting on supercomputers [3]. Today, WDEC refers to all pieces of the code. In the revamped WDEC, the user can choose whether to calculate periods or not, among other options.

WDEC revamped has easy-to-set flags that allow the user to see the original screen output and obtain all the output files old versions of the code used to write out.

The Nostalgic Corner

Figure 1 Comparison of periods found for a fiducial model (same input effective temperature, mass, and chemical profiles), calculated using the old EOS versus the MESA EOS. Top: l=1 modes, bottom: l=2 modes.

References

[1] Lamb, D.Q. & van Horn, H.M., 1975, ApJ, 200, 306 [2] Kawaler, S.D., Winget, D.E. & Hansen, C.J. 1985, ApJ, 295, 547 [3] Metcalfe, T.S., & Charbonneau, P. 2003, Journal of Computational Physics, 185, 176 [4] Paxton, B., Bildsten, L., Dotter, A., et al. 2011, ApJS, 192, 3 [5] http://evolgroup.fcaglp.unlp.edu.ar/TRACKS/PULSATIONS/PULSATIONS_DA/ pulsations_cocore.html

Effect of Equations of State on the Periods